Martensitic antibacterial stainless steel and manufacturing method thereof

ABSTRACT

This invention relates to antimicrobial martensitic stainless steels with nano precipitation and their manufacturing method of melting, forging, heat treatment. As the nano ε-Cu phases are precipitated in the matrix dispersedly, the martensitic stainless steels have excellent antimicrobial properties. The martensitic stainless steels may comprise from 0.35 to 1.20 weight percent C, from 12.00 to 26.90 weight percent Cr, from 0.29 to 4.60 weight percent Cu, 0.27 weight percent as less Ag, from 0.15 to 4.60 weight percent W, from 0.27 to 2.80 weight percent Ni, from 0.01 to 1.125 weight percent Nb, from 0.01 to 1.35 weight percent V, 1.8 percent or less Mn, from 0.15 to 4.90 weight percent Mo, 2.6 weight percent or less Si, 3.6 weight percent or less RE (rare earth) and the balance Fe and incidental impurities.

PRIORITY

This application claims priority to Chinese Application No.201110083730.9 filed Apr. 2, 2011, the content of which is herebyincorporated by reference for its supporting teachings.

TECHNICAL FIELD

The invention relates to the interdisciplinary field of metal materialsand medical microbiology, and more specifically to a martensiticstainless steel and adding specific antibacterial alloying elements suchas copper and other metals to the martensitic stainless steel to havehomogeneous distribution and dispersion of nano-level precipitatedantibacterial phase ε-Cu in the substrate of martensite antibacterialstainless steel, leading to good antibacterial and mechanical propertiesof the martensitic stainless steel, and further relates to amanufacturing technology and method of the antibacterial martensiticstainless steel.

BACKGROUND ART

In recent years, world-wide bacterial infection events have repeatedlyoccurred, for example, the intestinal infectious diseases caused by O157 E. coli in 1996, which spread to 44 prefectures in Japan, infectingmore than 9,000 people; the Bovine spongiform encephalopathy (BSE)outbreak in Europe from mid-1980s to mid-1990s; SARS which first startedin Shunde, Guangdong, China in 2002 and quickly spread to Southeast Asiaand even the world, and was gradually eliminated in the mid-2003; avianinfluenza, which was first found to also infect human beings in 1997 inHong Kong, had severe outbreaks from December 2003 in many East Asiancountries, mainly Vietnam, Korea and Thailand, resulting in a number ofdeaths in Vietnam. In 2010, a British media reported that a new superbugNDM-1 was found in South Asia, and this super bacteria had a very strongresistance to medicines and was likely to spread to the world. In 2011,the infection with Listeria monocytogenes that first started in theUnited States threatened the lives of a large number of people, causingthe deaths of some of these people. The awareness in prevention of andfight against bacteria is growing in humans after many invasions bybacteria and viruses. Today, anti-bacteria has become a way of life forhuman beings.

Nearly a hundred years of development in stainless steel, various kindsof stainless steel products become increasingly popular among people.Therefore, there comes an antibacterial stainless steel with thestainless steel material itself having the antimicrobial properties, andthe martensite antibacterial stainless steel can be extensively used inmedical device, pharmaceutical equipment, food processing, beauty andhairdressing, knives and other industries.

It is well known that the elements such as copper and silver have astrong bactericidal effect. In recent decades, it has been found thatcopper can be very well used for medical purposes, for example, in1970s, the Chinese medical inventors Liu Tongqing and Liu Tongle foundin their research that copper had a strong anti-cancer function andsuccessfully developed an appropriate anti-cancer drug “Anti-cancer(Keai) 7851” which has achieved clinical success. Later, a Mexicanscientist also found that copper has anti-cancer function. It isbelieved that copper will make greater contributions to improvinghuman's health in the near future.

Adding an appropriate amount of copper, silver and other antimicrobialalloying elements into the martensitic stainless steel and a specialantimicrobial treatment allows a homogeneous distribution and dispersionof nano-level granular precipitated antibacterial phase ε-Cu in thesubstrate of martensite antibacterial stainless steel, leading to goodantibacterial and mechanical properties of the martensitic stainlesssteel. The experimental results show that adding copper and silver canrefine the stainless steel crystal grains.

The antibacterial principle of antibacterial martensitic stainless steelis: after the non-level granular precipitated antibacterial phase thatis uniformly dispersed and distributed is chromatographed from the metalsurface, it contacts bacteria, and damages the cell membrane by actingon the cell, coagulating the proteins of the bacteria or damaging theDNA thereof, and destroying the normal tissues of bacterial cells andthe balance of cell multiplying, so as to prevent bacterial growth andreproduction or eliminate the bacteria.

Antibacterial stainless steel was first proposed and invented in Japanat the end of last century. In the United States, although the work onantibacterial stainless steel starts at a later time, the principles andmanufacturing techniques and methods have been basically grasped so far.At present, austenite antibacterial stainless steel, ferriteantibacterial stainless steel and antibacterial martensitic stainlesssteel achieve the antibacterial effect and are gradually accepted bypeople by adding the antibacterial alloying elements such as copper orsilver during the stainless steel production process, and byantimicrobial treatment. For example, Japanese patents JPA H8-104952,JPA H9-170053 and JP99800249.6 proposed adding copper or silver directlyto stainless steel and antibiotic treatment, ultimately achieving alasting and good antibacterial effect; the stainless steel with copperand iron ferrite published in Chinese patent CN1498981 provides a goodantibacterial property to ferritic stainless steel by adding 0.4 to 2.2%weight % of copper which enables homogeneous distribution and dispersionof nano-level precipitated antibacterial phase ε-Cu in the substratethereof.

One objective of the present invention is to provide a martensiticantibacterial stainless steel.

Another objective of the present invention is to provide a manufacturingtechnique and method for smelting, forging and heat treatment of saidmartensitic antibacterial stainless steel.

DESCRIPTION OF THE INVENTION

One objective of the present invention is to provide anano-precipitation phase martensitic antibacterial stainless steel. Thenano-level precipitated antibacterial phase ε-Cu is homogeneouslydistributed and dispersed in the substrate of martensitic stainlesssteel, providing good antibacterial and mechanical properties of themartensitic stainless steel.

A martensitic antibacterial stainless steel of the present invention,wherein:

The chemical compositions of the stainless steel (by weight percent)are: C: 0.35-1.20 weight %, Cr: 12.00-26.90 weight%, Cu: 0.29-4.60weight %, Ag≦0.27 weight %, W: 0.15-4.60 weight %, Ni: 0.27-2.8 weight%, Nb: 0.01-1.25 weight %, V: 0.01-1.35 weight %, Mn≦1.8 weight %, Mo:0.15-4.90 weight %, Si≦2.6 weight %, RE≦3.6 weight %, and remainders areFe and unavoidable impurities.

In order to improve the integrated properties of the antibacterialmartensitic stainless steel, in a preferred embodiment, said martensiteantibacterial stainless steel also contains one or more elementsselected from: Ti≦0.8 weight %, Zr≦0.8 weight %, Sn≦0.8 weight %,Co≦1.25 weight %.

In order to improve the ageing enhanced role, tempering stability andenhanced secondary hardening effect of martensite antibacterialstainless steel and to enhance the corrosion resistance, said martensiteantibacterial stainless steel further contains one or more elementsselected from: Al<3.45 weight %, N<0.15 weight %.

The major chemical compositions and ingredients of martensiteantibacterial stainless steel of the present invention are described indetails below. C: In martensite antibacterial stainless steel, carbon isan important element that is also an austenite forming element with a30-fold austenite formation capacity as compared to nickel. In order tomake the steel with a “stainless” requirement for stainless steel, thechromium content required is ≧12 weight %. However, as for iron-chromiumalloy, such chromium content closes the γ phase, making martensiticstainless steel into a single ferrite microstructure, and not producemartensitic transformation by heat treatment. In order to producemartensitic transformation, carbon content should change between 0.1weight % and 1.2 weight %.

When C content is controlled between 0.35 to 0.96 weight %, it canachieve the objective of increasing the alloy strength while maintaininga good processability; when carbon content is below 0.10 weight % in thealloy, it seldom reach the strength of the alloy; when carbon content ishigher than 1.20 weight %, it will not reduce the corrosion resistance,but greatly increase the processing and manufacturing difficulty, andeven make it difficult for processing. Therefore, under normalcircumstances, preferably C content is between 0.35 and 0.96 weight %.

Cr: Chromium is a ferrite forming element, and a sufficient amount ofchromium can make antibacterial martensitic stainless steel into asingle ferritic stainless steel. The interaction of chromium and carbonin the martensite antibacterial stainless steel makes it have a stableγ-phase or γ+α phase region at a high temperature. In order to producetransformation of martensite antibacterial stainless steel in quenching,there is an interdependent relationship between chromium and carbon,expanding the γ phase region while the solubility limit of carbon isreduced with the increase of chromium content. For example, in theiron-chromium-carbon alloy with carbon content of 0.6 weight %, chromecontent is up to 18 weight % and it maintains a pure austenite even at ahigh temperature; when Cr content is higher than 18 weight % ofchromium, the steel will composed of two-phase compositions ferrite andaustenite; when Cr content is higher than 27 weight %, the antibacterialmartensitic stainless steel will become the single ferritemicrostructure.

However, martensite antibacterial stainless steel must have the chromiumcontent of ≧12 weight %, and only the content of 12 weight % or more canmake the stainless steel. When the chromium content is <12 weight %, itcannot be called as a stainless steel; in the martensite antibacterialstainless steel, when chromium content is 30 weight % or even more thanthat, the antibacterial martensitic stainless steel will become thesingle ferrite composition but not a martensitic stainless steel, and itcannot produce martensitic transformation by heat treatment either.Although in the martensite antibacterial stainless steel, γ circle canbe moved to the direction of high chromium by adding Ni, martensiticstainless steel will still become a single ferrite composition when thechromium reaches 30 weight %. Because when Ni content exceeds 4.3 weight% in the antibacterial martensitic chrome-nickel stainless steel, itwill no longer have effect on y circle, at this time, the chromiumcontent remains <30 weight %.

Ni: in order to improve the integrated performance of the antibacterialmartensitic stainless steel, nickel is added to martensitic chromiumantibacterial stainless steel to form a martensitic chrome-nickelantibacterial stainless steel. Nickel is a γ-phase forming element thatexpands the austenite stability region. Nickel affects γ phase ofiron-chromium alloy as: with the increase of nickel content in steel, γcircle will move to the direction of high chromium, which means thatchromium in the martensite antibacterial stainless steel can improve butnot form a single iron ferrite composition. However, when Ni reaches acertain value, it will no longer have effects on chromium.

Because nickel expands the γ and α+γ phase regions of iron-chrome alloy,it enables low-carbon iron-chromium alloy with the quenching ability, orpresence of carbon can make the chromium content of low-carbon (<0.15weight % C) martensite stainless steel move to a higher level, improvingthe corrosion resistance of steel. The nickel content cannot be too highin antibacterial martensitic chrome-nickel stainless steel, otherwise,the dual effect of nickel expansion in γ phase region and reduced Mstemperature will make the steel become a single-phase austeniticstainless steel or lose the quenching ability.

Another important role of nickel is to reduce δ ferrite content in thesteel, which is an element with the best effect among all alloyingelements.

Cu: Copper is an austenite forming element. In martensite antibacterialstainless steel, copper is first added to martensitic stainless steel asan antimicrobial basic element. When Cu<0.29 weight %, martensiticstainless steel has a very poor antibacterial effect and even loses theantibacterial effect; when Cu<1.00 weight %, the antibacterial effect isstill not ideal; Cu>5.90 weight %, the thermal processing of martensiteantibacterial stainless steel becomes more difficult while the machiningproperties and corrosion resistance are reduced, increasing the cost ofmartensite antibacterial stainless steel.

Ag: In the present invention, silver is added to the martensiticstainless steel as a very important effective complement to theantibacterial alloying element. As we all know, silver ions and silvercompounds can kill or inhibit bacteria, viruses, algae and fungi, andsilver is also known as a pro-bio-metal because it has disease fightingeffects.

Silver has a strong bactericidal capacity. Three hundred years beforeChrist, when Alexander, Emperor of Greek Kingdom led a military conquestto the east, the army was infected by tropical dysentery, and most ofsoldiers were sick and died, he was forced to terminate the conquest.However, the Emperor and very few of officers were infected. The mysterywas not revealed until the modern times. The reason is that thetableware for the Emperor and officers was made of silver, while thesoldiers' tableware was made of tin. Silver can be decomposed in thewater to a very small amount of silver ion that can absorbmicroorganisms in water, making the enzyme that microorganisms rely onto breath lose its effect, thereby killing the microorganisms. Sliverions have a very strong bactericidal ability and several billionths ofmilligrams of silver can purify 1 kg of water.

RE: adding rare earth elements (Ce, La, etc.) into martensitic stainlesssteel will not only improve the thermoplastic of high-chromium-nickelstainless steel containing molybdenum and copper, and at the same time,rare earth elements are very useful for improving the thermal processingof chromium-nickel austenitic stainless steel.

In recent years, rare earth drugs are frequently studied. Currently,rare-earth compounds have been clinically used in some countries andhave played a very good effect on diagnosis and treatment of certaindiseases. Modern scientific research has shown that the rare earth andrare earth compounds have the following clinical pharmacologicaleffects:

The rare earth, such as cerium and other elements, have goodantibacterial and sterilization effects;

Rare earth drugs have a regulatory role on immune function after burn;

The rare earth compounds have strong in vitro and in vivo anticoagulanteffects;

Rare earth drugs have strong anti-allergic and anti-inflammatoryeffects. At present, they have been extensively used as a topicalanti-inflammatory drug in clinics and achieved satisfactory outcomes;

The rare earth elements have anti-tumor effect and can be used forcancer diagnosis. Rare earth stable isotope has the anticancer mechanismthat it can replace Ca++ and Mg++ at the cell or sub-cell structure(such as membrane and mitochondrial surface), resulting in irreversibleinjury to cells, and that a large amount of rare earth accumulated intumor cells destroys the exchange between Ca++, and Mg++, and even thecomposition that can be called as nucleus, thereby inhibiting tumordevelopment. More rare earth ion is accumulated in tumor cells than innormal cells because cancer cells have a high level of DNA and DNAphosphoryl have a higher affinity to rare earth ions, resulting in awide range of chelation;

The rare earth elements, such as lanthanum and cerium have a centralanalgesic effect.

W: Tungsten has a high melting point and great specific gravity, and isa precious metal alloying element. Tungsten and carbon forms a tungstencarbide with a high level of hardness and wear resistance, which is veryuseful for antibacterial martensitic stainless steel of the presentinvention.

Effect of W on the composition: it narrows the γ phase region to form γphase circle with the maximum solubility of 33 weight % and 3.2 weight %in α iron and γ iron, and W is a strong carbide and a nitride formingelement and tungsten carbide is hard and wear resistant;

Effect of W on the performance of martensitic stainless steel: tungstenhas the secondary hardening effect, provides a red hardness, andincreases the wear resistance. W has a similar effect on thehardenability, tempering stability, mechanical properties and heatresistance of the martensite antibacterial stainless steel, but it has aweaker effect than molybdenum when compared in molybdenum content byweight percentage.

The martensitic antibacterial stainless steel is widely used. During theuse of antibacterial martensitic stainless steel, in particular, when itis used for cutting tool products, it often requires good hardness andsharpness as well as good toughness, and further good wear resistance ofmartensite antibacterial stainless steel. Therefore, martensiteantibacterial stainless steel described in one embodiment of the presentinvention also selects W: 0.15 to 6.00 by weight %. Adding W greatlyimproves the wear resistance and hardenability of the martensiteantibacterial stainless steel.

Mo: molybdenum is a ferrite forming element and has the ability topromote α phase forming equivalent to chromium. In martensiteantibacterial stainless steel, in addition to improving the corrosionresistance martensitic antibacterial stainless steel, molybdenum has themajor effect to improve the strength and hardness of the martensiteantibacterial stainless steel and enhance the secondary hardening effectthereof.

For example, type A martensitic stainless steel has its chemicalcompositions, including: 0.72 weight % C, 15.7 weight % Cr; type Bmartensitic stainless steel has its chemical composition, including:0.55 weight % C, 13.5 weight % Cr, and 0.5 weight % Mo. Based on themutual restraint relationship of effect between chromium and carbon onhardness of martensitic stainless steel, if type B martensitic stainlesssteel does not contain molybdenum, type A and B martensitic stainlesssteels will be very close in hardness. Type B martensitic stainlesssteel containing 0.5 weight % Mo increases the hardness of type Bmartensitic stainless steel, particularly evident in the low-temperaturequenching, and this effect is very useful for antimicrobial martensiticstainless steel cutting tools.

Adding molybdenum into martensite antibacterial stainless steel canincrease the tempering stability and strengthen the secondary hardeningeffect, while increasing the hardness of martensite antibacterialstainless steel, but the toughness will not be reduced with theincreased hardness.

In the martensite antibacterial stainless steel, if the Mo content istoo low, it will be difficult to play its due effect; too highmolybdenum content will not only greatly increase the cost of martensiteantibacterial stainless steel, but also promote the formation of δferrite, causing adverse effects.

V: vanadium is an excellent deoxidizer of martensite antibacterialstainless steel. Adding 0.5 weight % vanadium in the martensiteantibacterial stainless steel can refine compositional crystal grainsand improve the strength and toughness. The carbide formed by vanadiumand carbon can increase the ability of hydrogen corrosion resistanceunder high temperature and pressure.

Effect of vanadium on composition: narrow the γ phase region and form γphase circle; infinite solid solution in α iron with a maximumsolubility in γ iron of approximately 1.35 weight %. Vanadium is astrong carbide and nitride forming element.

Effect of vanadium on martensite antibacterial stainless steelperformance: narrow the γ phase region and form γ phase circle; infinitesolid solution in α iron with a maximum solubility in γ iron ofapproximately 1.35 weight %. It is a strong carbide and nitride that canincrease the service life of the antibacterial martensitic stainlesssteel. Vanadium can increase the creep and rupture strength of theantibacterial martensitic stainless steel through the disperseddistribution of small carbide particles. When the vanadium and carboncontent (by weight) is greater than 5.7, it can prevent or mitigate theintergranular corrosion of medium of stainless acid resistant steel, andgreatly increase the ability of antibacterial martensitic stainlesssteel to resist high temperature, high pressure, hydrogen corrosion, canrefine the crystal grains, slow the transfer rate of the alloyingelements, but is adverse to high temperature oxidation of martensiteantibacterial stainless steel.

Co.: Cobalt is an austenite forming element, and has a similar role tonickel. In martensite antibacterial stainless steel, adding cobaltincreases the tempering stability, but has no significant effect onsecondary hardening. The results of study on 12 weight % Cr martensiticantibacterial stainless steel have shown that cobalt increases thehardness of martensite itself, with the main effect of solid solutionstrengthening, but without remarkable secondary hardening effect.

N: nitrogen has a similar effect to carbon, but does not produce adeleterious effect on the corrosion resistance; on the contrary, undercertain conditions, nitrogen can improve the corrosion resistance.Nitrogen has a greater strengthening effect than carbon on martensiticchrome-nickel antibacterial stainless steel and has a lower cost.

Al: Aluminum is a ferrite forming element and has ability of ferriteformation 2.5 to 3.0 times as that of chromium. Aluminum in martensiteantibacterial stainless steel is mainly to play the ageing strengtheningeffect, and improve the tempering stability and enhance secondaryhardening effect.

Ti: Titanium is similar to aluminum in the effect on martensiticantibacterial chrome-nickel stainless steel, and is often used inantibacterial ageing stainless steel. An appropriate amount of titaniumhas a significant ageing strengthening effect, but too high level oftitanium will reduce the impact toughness and plasticity of martensiteantibacterial stainless steel. In addition, titanium is a strongdeoxidizer in martensite antibacterial stainless steel. It can make theinternal composition of antibacterial martensitic stainless steel denseand refine the crystal grains, to reduce the ageing sensitivity and coldbrittleness and to improve the welding performance.

Nb: niobium can refine the crystal grains and reduce the thermalsensitivity and temper brittleness of steel to improve the strength, butreduce the plasticity and toughness. Adding niobium in the ordinarylow-alloy martensitic antibacterial stainless steel can improve theability to fight against atmospheric corrosion and anti-hydrogen,nitrogen and ammonia corrosion at a high temperature. Niobium canimprove the welding performance.

Zr: zirconium has an effect similar to niobium, titanium and vanadium inthe martensite antibacterial stainless steel. A small amount ofzirconium will have the effect of degassing, purification and crystalgrain refinement, be favorable to low-temperature toughness ofmartensitic antibacterial stainless steel, and can eliminate the ageingphenomenon, and improve the stamping performance of martensiteantibacterial stainless steel.

Another aspect of the present invention also provides a smeltingtechnology and method for martensite antibacterial stainless steel:

The present invention provides a method for smelting martensiticantibacterial stainless steel because the present invention uses copperas an antimicrobial element and the copper has a lower melting point.Cooper has a melting point of 1,083.4±0.2° C., so it is volatile duringthe smelting process. During the melting process of martensiteantibacterial stainless steel, the raw materials but copper should befirst smelt in furnace, and after the raw materials are smelt, thecooper is added and quickly heated to 1,680° C. or less for castingingot. Ingot should not have the defects, such as sticky sand, airholes, gravel, slag. After ingot casting is completed, annealingtreatment is needed for ingot.

The present invention also provides a forging method for martensiticantibacterial stainless steel. After martensite antibacterial stainlesssteel is smelted and annealed, the ingot should be forged, the forgingstate of ingot composition should be forged into a wrought state.Because forging can eliminate the defects such as loose cast occurringduring the smelting process by forging, optimize the microstructure andmaintain a complete flow line of metal, it will necessarily havesuperior mechanical properties than the forgings of the same materials.The specific forging method is as follows: first slowly and fully heatthe ingot at a speed of not more than 20° C./s; heat the ingot to atemperature not more than 1,350° C.; the initial forging temperatureshould be ≦1,300° C., and final forging temperature should be ≧850° C.

After the martensite antibacterial stainless steel is forged, theforgings should be subject to spheroidization treatment with themethods: heat the forgings to 960° C. or less, preferably 750-950° C.and maintain the temperature for <36 hours, preferably for 12 to 24hours.

If martensite antibacterial stainless steel plate is finally needed, themartensite antibacterial stainless steel is forged and annealed, andthen is hot-rolled, cold rolled and annealed.

The present invention also provides a heat treatment method formartensitic antibacterial stainless steel. Heat treatment is a veryimportant aspect of production during the manufacturing process ofmartensite antibacterial stainless steel, and it directly affects themechanical properties and antibacterial properties of antibacterialmartensitic stainless steel. The heat treatment method is as follows:first quench the antibacterial martensitic stainless steel, and afterquenching, perform deep cryogenic treatment on martensite antibacterialstainless steel. After the deep cryogenic treatment is complete, performtempering for martensite antibacterial stainless steel at a quenchingtemperature of 1,000-1,100° C. The deep cryogenic treatment is performedat a temperature of −45° C. to −196° C. and tempering is performed at atemperature of 160-650° C.

At time of martensite antibacterial stainless steel heat treatment, keepthe temperature maintaining time, deep cryogenic treatment time andtempering time all for ≦4 hours in the quenching furnace. Afterantibacterial martensitic stainless steel is subject to heat treatment,it has a hardness of: tempering martensite: 46-62 HRC.

The present invention also provides a manufacturing method ofmartensitic antibacterial stainless steel, consisting of followingsteps: first select and determine the alloy composition of specificcomponent based on the use of antimicrobial martensitic stainless steel,and then place it in the furnace for smelting. In the smelting furnace,first melt the raw materials other than copper, and then add copper andheat it quickly to 1,680° C. or less for casting ingot, and annealing isperformed after completion of casting; following that, forge the ingotafter forging and annealing. Before forging, the ingot should be firstfully heated before forging again. At time of heating, the heating ratemust not exceed 20° C./s, the heating temperature should ≦1,350° C.,initial forging temperature should ≦1,300° C. and final forgingtemperature should ≧850° C. The martensite antibacterial stainless willbe subject to spheroidization treatment after forging. At time of heattreatment of martensite antibacterial stainless steel, quenching shouldbe first performed on martensite antibacterial stainless steel and thendeep cryogenic treatment and tempering should be performed. Quenchingtemperature should be 1,000-1,100° C., deep cryogenic treatmenttemperature should be −45 to −196° C. and tempering temperature shouldbe 160-650° C. At time of martensite antibacterial stainless steel heattreatment, keep the temperature maintaining time, deep cryogenictreatment time and tempering time of martensite antibacterial stainlesssteel all for ≦4 hours in the quenching furnace. After antibacterialmartensitic stainless steel is subject to heat treatment, it has ahardness of: tempering martensite: 46-62 HRC.

Specific Embodiments EXAMPLE 1

The chemical compositions are: C: 0.36 weight %, Cr: 12.10 weight %, Cu:1.57 weight %, Ni: 2.48 weight %, Mn: 0.69 weight %, Si: 0.67 weight %,Mo: 0.63 weight %, P: 0.013 weight %, S: 0.011 weight %, V: 0.01 weight%, W: 0.17 weight %, Ti: 0.35 weight %, Zr: 0.26 weight%, Co: 0.07weight % Nb: 0.35 weight %, and the remainder is Fe. First, place theraw materials other than copper in the smelting furnace for melting andsmelting, and then add copper and heat it quickly to 1,680° C. or lessfor casting ingot, and annealing is performed after completion ofcasting; following that, forge the ingot after forging and annealing.Before forging, the ingot should be first fully heated before forgingagain. At time of heating, it is determined that the heating rate shouldbe within 20° C./s, the heating temperature should ≦1,350° C., initialforging temperature should ≦1,300° C. and final forging temperatureshould ≧850° C. The martensite antibacterial stainless will be subjectto spheroidization treatment after forging. At time of heat treatment ofmartensite antibacterial stainless steel, quenching should be firstperformed on martensite antibacterial stainless steel and then deepcryogenic treatment and tempering should be performed. Quenchingtemperature should be 1050° C., deep cryogenic treatment temperatureshould ≦−196° C. and tempering temperature should be ≦650° C. At time ofmartensite antibacterial stainless steel heat treatment, keep thetemperature maintaining time, deep cryogenic treatment time andtempering time of martensite antibacterial stainless steel all for ≦4hours in the quenching furnace; and then cut the cold-rolled stainlesssteel plate into 50×50×2.0 mm sample plate for testing the performanceof martensitic stainless steel.

With 3Cr13Mo as the control material, the chemical composition analysisresults of martensite antibacterial stainless steel made in this exampleand reference material 3Cr13Mo are shown in Table 1.

TABLE 1 (main chemical composition analysis results of martensiteantibacterial stainless steel and the reference material) Martensiticstainless steel C Cr Cu Ni Mn Si Mo Nb V W Ti Example of 0.36 12.10 1.572.48 0.69 0.67 0.63 0.35 0.01 0.17 0.35 present invention (weight %)Martensitic antibacterial stainless steel Example of 0.32 13.0 — ≦0.6≦1.0 ≦0.8 ≦0.75 — — — — control (weight %) 3Cr13Mo

Antibacterial Performance Tests

1. Antibacterial performance test has been conducted by ShanghaiInstitute of Industrial

Microbiology, China (CNAS L1483 MA2010090430Q) with the testing methodsas follows: adopted standard: JIS Z 2801-2000; selected strains:Escherichia coli (ATCC8739), Staphylococcus aureus (AS1.89). The testresults are shown in Table 2.

TABLE 2 (test results of performance of martensitic antibacterialstainless steel in the present example) Escherichia coli (ATCC8739)Staphylococcus aureus (AS1.89) 0 hour 24 hours 0 hour 24 hours NumberNumber 24 hours Number Number 24 hours of of Antibacterial of ofAntibacterial colonies colonies rate colonies colonies rate Sample name(CFU) (CFU) (%) (CFU) (CFU) (%) Martensitic 3.6 × 10⁵ <10 >99.9 3.8 ×10⁵ <10 >99.9 antibacterial stainless steel

The antibacterial rate of 3Cr13Mo martensitic stainless steel on E.coli, and Staphylococcus aureus=0 (no antibacterial effect)

6. Antibacterial persistence test

The surface is martensite antibacterial stainless steel is rubbed off0.5 mm (simulating the wear after a long-term use), then the grindedmartensitic antibacterial stainless steel is wrapped firmly with a clothwith water and placed in a kitchen at an ambient temperature of 35°C.-38° C. (kitchen is a place with bacteria breeding at a fast speed andat a fastest one at an ambient temperature of 35° C. to 38° C.) for oneweek, and then it is taken out and placed and dried for 30 min beforethe antibacterial test on the antibacterial stainless steel. The testmethod is as follows:

Lamination method is used, and Escherichia coli and Staphylococcusaureusa are used as experimental bacteria; the experimental proceduresare as follows:

1) Place experiment sample (martensite antibacterial stainless steel)washed by ethanol and the reference sample (3Cr13Mo) at the temperatureof 121 ±1° C. for high temperature sterilization for 20 minutes;

2) Dilute the inoculated bacteria with PBS solution (0.03 mol/l, pH=7.2,disodium hydrogen phosphate 2.83g, potassium dihydrogen phosphate 1.36g, distilled water 100 ml) into a bacterial solution at the standardconcentration of 10⁵, evenly drip 0.5 ml bacterial solution onmartensite antibacterial stainless steel samples and control samples(3Cr13Mo) and are respectively covered with sterile plastic film;

3) Place martensite antibacterial stainless steel samples and thecontrol stainless steel samples with the surfaces coated with bacterialsolution into an incubator at the temperature of 35° C. and humidity of90% for 24 h.

4) Place it in the incubator at 35° C. for 24 h and 48 h using the platemethod (agar culture method). Finally, calculate the number of bacteriaand antibacterial rate from the plastic plate.

5) The process is repeated three times for each specie and sample, andthe mean value is used.

In present example, the antibacterial test results of martensiticantibacterial stainless steel are shown in Table 2. The antibacterialrate is calculated with the formula:

${{Antibacterial}\mspace{14mu} {rate}\mspace{14mu} (\%)} = {{\frac{\begin{matrix}{{{Count}\mspace{14mu} {of}\mspace{14mu} {bacteria}\mspace{14mu} {on}\mspace{14mu} {the}\mspace{14mu} {control}\mspace{14mu} {stainless}\mspace{14mu} {steel}} -} \\{{count}\mspace{14mu} {of}\mspace{14mu} {bacteria}\mspace{14mu} {on}\mspace{14mu} {the}\mspace{14mu} {antibacterial}\mspace{14mu} {stainless}\mspace{14mu} {steel}}\end{matrix}}{{Count}\mspace{14mu} {of}\mspace{14mu} {bacteria}\mspace{14mu} {on}\mspace{14mu} {the}\mspace{14mu} {control}\mspace{14mu} {stainless}\mspace{14mu} {steel}}100}\%}$

Wherein, the count of bacteria on the control stainless steel refers tothe number of viable bacteria after culture experiment has beenconducted for the control stainless steel, and the count of bacteria onthe antibacterial stainless steel refers to viable bacteria afterculture experiment has been conducted for the antibacterial stainlesssteel.

The test of antimicrobial martensitic stainless steel shows E. coli andStaphylococcus aureus has an antibacterial rate >99.9%

The antibacterial rate of 3Cr13Mo martensitic stainless steel on E.coli, and Staphylococcus aureus=0 (no antibacterial effect).

EXAMPLE 2

The chemical compositions are: C: 0.71 weight %, Cr: 23.1 weight %, Cu:3.97 weight %, Ni: 3.76 weight %, Mn: 0.69 weight %, Si: 0.67 weight %,Mo: 0.71 weight %, P: 0.015 weight %, S: 0.016 weight %, V: 1.29 weight%, W: 1.87 weight %, Ti: 0.35 weight %, Co: 0.07 weight %, Sn: 0.3weight %, Al: 1.15 weight %, Nb: 0.75 weight %, and the remainder is Fe.

Same as example 1, first perform the smelting, forging, hot rolling,cold rolling and annealing of martensitic stainless steel, and then cutthe cold-rolled stainless steel plate into 50×50×2.0 mm sample plate fortesting the performance of martensitic stainless steel.

Antibacterial treatment of martensitic stainless steel test sample ofthe present example: first place the test sample plate into the heatingfurnace and heat it to 1,060° C., then keep the temperature for 4 hoursor less and cool it to room temperature to ensure that Cu can be fullydissolved in the substrate of martensitic stainless steel; after that,place the test sample plate into the heating furnace and heat it to 580°C. or less for temperature maintaining for 4 hours or less, and aftertemperature maintaining, cool martensitic antibacterial stainless steelto room temperature.

With 7Cr17 as the control material, the chemical composition analysisresults of martensite antibacterial stainless steel made in this exampleand reference material 7Cr17 are shown in Table 3.

TABLE 3 (main chemical composition analysis results of martensiteantibacterial stainless steel and the reference material) Martensiticstainless steel C Cr Cu Ni Mn Si Mo Nb V W Al Example of 0.71 23.1 3.973.76 0.69 0.67 0.71 0.75 1.29 1.87 1.15 present invention (weight %)Martensitic antibacterial stainless steel Example of 0.68 17.00 — ≦0.6≦1.0 ≦1.0 ≦0.75 — — — — control (weight %) 7Cr17

Antibacterial Performance Tests

Antibacterial performance tests are conduced in the same way asdescribed in example 1. The test shows that its antibacterialperformance is consistent with that in example 1. The test results are:

The antibacterial rate of antimicrobial martensitic stainless steel onE. coli and Staphylococcus aureus in the present example=99.9%

The antibacterial rate of 7Cr17 martensitic stainless steel on E. coli,and Staphylococcus aureus=0 (no antibacterial effect).

Mechanical Performance

The mechanical performance of martensitic antibacterial stainless steelin the present example and 7Cr17 martensitic stainless steel arerepeatedly tested and the results of mechanical performance analysis areshown in Table 4.

TABLE 4 (test results of mechanical performance of martensiticantibacterial stainless steel in the present example and 7Cr17martensitic stainless steel) Mechanical performance martensiticstainless steel after annealing Hardness HRC Martensitic Yield strengthTensile strength Elongation (Tempered stainless steel σ_(0.2)/MPaσ_(b)/MPa rate σ₅/% martensite) Martensitic antibacterial ≧265 ≧650≧16.3 57 stainless steel of the present example 7Cr17 Martensitic ≧245≧590 ≧15 55 stainless steel

EXAMPLE 3

The chemical compositions are: C: 0.96 weight %, Cr: 15.10 weight %, Cu:3.67 weight %, Ni: 3.68 weight %, Mn: 0.69 weight %, Si: 0.67 weight %,Mo: 4.59 weight %, P: 0.015 weight %, S: 0.012 weight %, N: 0.09 weight%, V: 0.12 weight %, Nb: 0.95 weight %, W: 3.65 weight %, and theremainder is Fe.

Same as example 1, first perform the smelting, forging, hot rolling,cold rolling and annealing of the martensitic antibacterial stainlesssteel, and then make the martensitic antibacterial stainless steel intoa sample plate for testing, and following that, perform theantibacterial treatment for said sample plate.

With 9Cr18MoV as the control material, the chemical composition analysisresults of martensite antibacterial stainless steel made in this exampleand reference material 9Cr18MoVare shown in Table 5.

TABLE 5 (main chemical composition analysis results of martensiteantibacterial stainless steel and the reference material) Martensiticstainless steel C Cr Cu Ni Mn Nb Si Mo V W Example of present 0.96 15.103.67 3.68 0.69 0.95 0.67 4.59 0.12 3.65 invention (weight %) Martensiticantibacterial stainless steel Example of control 0.90 18.00 — ≦0.6 ≦1.0— ≦1.0 ≦0.55 0.10 — (weight %) 9Cr18MoV

Antibacterial Performance Tests

Antibacterial performance tests are conduced in the same way asdescribed in example 1. The test shows that its antibacterialperformance is consistent with that in example 1. The test results are:

The antibacterial rate of antimicrobial martensitic stainless steel onE. coli and Staphylococcus aureus in the present example=99.9%

The antibacterial rate of 9Cr18MoV martensitic stainless steel on E.coli, and Staphylococcus aureus=0 (no antibacterial effect).

EXAMPLE 4

Determine the martensitic stainless steel with the main chemicalcomposition of 0.72 weight % C and 15.7 weight % Cr as type A steel;Determine the martensitic stainless steel with the main chemicalcomposition of 0.55 weight % C and 13.5 weight % Cr and 0.5 weight % Moas type B steel; Determine the martensitic stainless steel with the mainchemical composition of 11.3 weight % C, 12.5 weight % Cr, 1.8 weight %Mo, 0.99 weight % Co and 1.36 weight % W as type C steel. In the presentinvention, test is conducted respectively types A, B and C steel and thecomparison is also conducted.

The comparison of type A steel and type B steel shows that if type Bmartensitic stainless steel does not contain molybdenum, type A and Bmartensitic stainless steel should have a very close hardness value.However, type B martensitic stainless steel containing 0.5 weight % Moincreases the hardness of type B martensitic stainless steel,particularly evident in the low-temperature quenching, and this effectis very useful for stainless steel cutting tools. Because type Cmartensitic stainless steel contains 1.36 weight % W and 0.99% weightCo., greatly improving the wearing resistance of type C steel, thecomparative analysis results for types A, B and C steels are shown inTable 6.

TABLE 6 Comparative analysis results for types A and B steels Type Csteel 1.23 weight % C Type B steel 12.5 weight % Cr Martensitic Type Asteel 0.55 weight % C 1.8 weight % Mo stainless 0.72 weight % C 13.5weight % Cr 15.7 weight % Co steel 15.7 weight % Cr 0.5 weight % Mo 1.36weight % W Hardness + ++ +++ Wear resistance + ++ +++

EXAMPLE 5

Determine the martensitic stainless steel with the main chemicalcomposition of 0.92 weight % C and 15.7 weight % Cr as type A steel;Determine the martensitic stainless steel with the main chemicalcomposition of 0.95 weight % C and 21.5 weight % Cr, 2.89 weight % Niand 0.5 weight % Mo as type B steel; Determine the martensitic stainlesssteel with the main chemical composition of 11.8 weight % C, 25.5 weight% Cr, 4.35 weight % Mo, 0.99 weight % Co and 5.26 weight % W as type Csteel. In the present invention, tests have been respectively conductedfor types A, B and C steels, the steels are made into knife for chef andthe comparison is conducted for the sharpness, wear resistance and etc.for the kitchen knife. The comparison results are shown in Table 7.

TABLE 7 Comparative analysis results for types A, B and C steelsMartensitic Sharpness Wear resistance stainless steel Used for 3 monthsUsed for half a year Used for 3 months Used for half a year Type A steelBlunt requiring Blunt requiring An obvious white An obvious white forgrinding for grinding line on knife blade line on knife blade Type Bsteel Staring to become blunt, Blunt requiring A white line on Anobvious white but being able to cut for grinding knife blade line onknife blade Type C steel Sharp without the Staring to become blunt,Difficult to see the A white line on need for grinding but being able tocut white line on knife blade knife blade Notes: 1. Because theprofessional chef frequently used the cooking knife to cut foods, a chefis often not willing to change a good cooling knife; 2. As for thesharpness of a kitchen knife, when the cooking knife becomes blunt, thechef will use a sharpening steel or whetstone or even grinding wheel togrind it in order to restore the sharpness; 3. As for the wearresistance of a kitchen knife, when the cooking knife blade has a whiteline, it indicates that the cooking knife is worn and needs grinding inorder to restore its sharpness.

Note: 1. Because the professional chef frequently used the cooking knofeto cut foods, a chef is often not willing to change a good coolingknife.

2. As for the sharpness of a kitchen knife, when the cooking knifebecomes blunt, the chef will use a sharpening steel or whetstone or evengrinding wheel to grind it in order to restore the sharpness;

3. As for the wear resistance of a kitchen knife, when the cooking knifeblade has a white line, it indicates that the cooking knife is worn andneeds grinding in order to restore its sharpness.

EXAMPLE 6

Determine the martensitic stainless steel with the main chemicalcomposition of 0.32 weight % C and 15.7 weight % Cr as type A steel;determine the martensitic stainless steel with the main chemicalcomposition of 0.35 weight % C, 30.00 weight % Cr and 0.56 weight % Nias type B steel. In the present invention, tests have been respectivelyconducted for types A and B steels, the steels are made into knife forchef and the comparison is conducted for the hardness, sharpness andetc. for the kitchen knife. The comparison results are shown in Table 8:

Comparative analysis results for types A and B steels Stainless steelHardness Sharpness Type A steel ✓ ✓ Type B steel x x Note: “✓” indicatesYes; “x” indicates No.

The reason that type B steel has zero hardness and sharpness is that theweight of Cr reaches up to 30.00% in the chemical composition of type Bsteel, making type B steel into a single ferrite microstructure ratherthan a martensitic stainless steel, while being unable to producemartensitic transformation by heat treatment.

What is claimed is:
 1. An antimicrobial martensitic stainless steelcomprising from 0.35 to 1.20 weight percent C, from 12.00 to 26.90weight percent Cr, from 0.29 to 4.60 weight percent Cu, 0.27 weightpercent or less Ag, from 0.15 to 4.60 weight percent W, from 0.27 to2.80 weight percent Ni, from 0.01 to 1.25 weight percent Nb, from 0.01to 1.35 weight percent V, 1.8 weight percent or less Mn, from 0.15 to4.90 weight percent Mo, 2.6 weight percent or less Si, 3.6 weightpercent or less RE(rare earth) and the balance Fe and incidentalimpurities.
 2. An antimicrobial martensitic stainless steel according toclaim 1, wherein the stainless steel contains one or more selected formthe group consisting of 1.25 weight percent or less Co, 0.8 weightpercent or less Ti, 0.8 weight percent or less Zr, 0.8 weight percent orless Sn.
 3. An antimicrobial martensitic stainless steel according toclaim 1, wherein the stainless steel further contains one or moreselected form the group consisting of less 3.45 wt. % Al and less0.15wt. % N.
 4. An antimicrobial martensitic stainless steel accordingto claim 1, wherein the Cr comprises from 14.7 to 23.8 weight percent.5. An antimicrobial martensitic stainless steel according to claim 1,wherein the C comprises from 0.45 to 0.96 weight percent.
 6. Anantimicrobial martensitic stainless steel according to claim 1, whereinthe Ni comprises from 0.31 to 1.9 weight percent.
 7. An antimicrobialmartensitic stainless steel according to claim 1, wherein the Wcomprises from 0.3 to 4.0 weight percent.
 8. A melting method for theantimicrobial martensitic stainless steels, comprising the steps of:melting from 0.35 to 1.20 weight percent C, from 12.00 to 26.90 weightpercent Cr, 0.27 weight percent or less Ag, from 0.15 to 4.60 weightpercent W, from 0.27 to 2.80 weight percent Ni, from 0.01 to 1.25 weightpercent Nb, from 0.01 to 1.35 weight percent V, 1.8 weight percent orless Mn, from 0.15 to 4.90 weight percent Mo, 2.6 weight percent or lessSi, 3.6 weight percent or less RE(rare earth) and the balance Fe andincidental impurities in a furnace to create an initial material; adding0.29 to 4.60 weight percent Cu to the initial material; quickly heatingthe initial material with the Cu to 1680 degrees centigrade; casting thematerial with the Cu as an ingot; and annealing the ingot.
 9. The methodof claim 8, further comprising the step of forging/rolling the annealedingot.
 10. The method of claim 9, wherein the forging/rolling comprisesthe steps of: heating the ingot uniformly at a rate of 20 degreescentigrade per second but not exceeding a temperature of 1350 degreescentigrade;
 11. The method of claim 10, wherein a starting temperatureis no more than 1300 degrees centigrade.
 12. The method of claim 10,wherein a finishing temperature is no less than 1300 degrees centigrade.13. The method of claim 10, wherein the forging/rolling isspheroidization-annealed at temperature from 750 degrees centigrade to950 degrees centigrade for 12-24 hrs.
 14. The method of claim 9, furthercomprising a heat-treatment method.
 15. The method of claim 14, whereinthe heat-treatment method comprises the steps of: quenching the steel attemperatures from 1000 degrees centigrade to 1100 degrees centigrade fora period no more than 4 hrs;
 16. The method of claim 15, wherein thesteel is then cryogenic-treated at temperature from −45 degreescentigrade to −196 degrees centigrade for a period no more than 4 hrs.17. The method of claim 16, wherein the steel is tempered at temperaturefrom 160 degrees centigrade to 650 degrees centigrade for a period nomore than 4 hrs.
 18. A method of producing antimicrobial martensiticstainless steel comprising the steps of: (1) completely melting from0.35 to 1.20 weight percent C, from 12.00 to 26.90 weight percent Cr,0.27 weight percent or less Ag, from 0.15 to 4.60 weight percent W, from0.27 to 2.80 weight percent Ni, from 0.01 to 1.25 weight percent Nb,from 0.01 to 1.35 weight percent V, 1.8 weight percent or less Mn, from0.15 to 4.90 weight percent Mo, 2.6 weight percent or less Si, 3.6weight percent or less RE(rare earth) and the balance Fe and incidentalimpurities in a furnace to create an initial material; adding 0.29 to4.60 weight percent Cu to the initial material to create a molten metal;heating the molten metal to 1680 degrees centigrade quickly and castingthe molten metal as an ingot; annealing the ingot; forging/rolling theingot by heating it uniformly at a rate of 20 degrees centigrade persecond; and wherein the heating temperature is no more than 1350 degreescentigrade; the starting temperature is no more than 1300 degreescentigrade; and the finishing temperature is no less than 1300 degreescentigrade; spheroidization-annealing the forged ingot at temperaturefrom 750 degrees centigrade to 950 degrees centigrade for 12-24 hrs tocreate a steel; heat-treating the steel by quenching it at a temperatureof from 1000 degrees centigrade to 1100 degrees centigrade for a periodno more than 4 hrs; cryogenically treating the steel at a temperature offrom −45 degrees centigrade to −196 degrees centigrade for a period nomore than 4 hrs; tempering the steel at a temperature of from 160degrees centigrade to 650 degrees centigrade for a period no more than 4hrs.